Unit 04 · The Clam or Squid
This is your first mollusk, and its soft body is protected — a clam behind two hinged valves, a squid inside its mantle. The challenge is getting in without wrecking what you came to see: parting the shell or opening the mantle to reveal the cavity beneath, then reading a body plan built for a life in water. The work is technique and careful observation — a patient entry, looking before you disturb anything, then locating and naming structures and explaining what each one does. An instructor watches you work, and the specimen — opened cleanly, structures intact — is the proof.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Instrument handling & safe technique | Forces the shell open or slashes through the mantle, destroying the soft parts inside. | Opens the shell or mantle with reminders but still cuts too deep and nicks the organs. | Holds each instrument the right way and opens the shell or mantle with shallow, controlled cuts that spare the soft parts, safely for both the student and the specimen. |
| Careful exposure & observation of the mantle cavity | Tears into the mantle cavity and disturbs the organs before looking at them. | Opens the mantle cavity roughly but disturbs the gills or gut before observing their layout. | Opens the mantle cavity cleanly along the correct line and observes the arrangement of structures before disturbing anything. |
| Locating & naming external structures | Cannot point to the shell or mantle, the foot, or the siphons. | Finds a few external parts with prompting but confuses the foot, siphons, or (for a squid) the arms and tentacles. | Locates and names the external structures on the specimen — shell or valves, mantle, foot, and siphons; or for a squid the mantle, arms, tentacles, funnel, and eyes. |
| Locating & naming internal structures | Guesses at the organs or names the wrong ones once the specimen is open. | Finds the larger organs but cannot reliably distinguish the gills from the gut or trace the adductor muscles. | Locates and names the internal structures on the specimen — gills (ctenidia), gut, and adductor muscles; or for a squid the pen, ink sac, and beak. |
| Explaining structure & function (and specimen care) | Cannot say what a structure does, and lets the specimen dry out or handles it carelessly. | Explains one or two structures' functions but not the rest, and keeps the specimen moist only when reminded. | Explains why key structures do their jobs — the gills drawing oxygen from water as the clam filter feeds, the squid’s funnel driving jet propulsion — while keeping the specimen moist, handling it respectfully, and cleaning up afterward. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“I worked the blade between the valves and cut the adductor muscles — that’s what holds the shell shut — so it opened without tearing the body. These feathery structures are the gills; water passes over them and the clam filters food out of it at the same time. On a squid the funnel is how it moves: it pushes water out through it and jets backward.”
“I kind of pried it apart and something ripped. I think this is the stomach? Or the gills? It’s all torn up now, so I’m not really sure which is which.”
You demonstrate this unit by doing the dissection while an instructor watches — opening, exposing, and naming real structures and explaining their function on your own specimen, not a written test. A criterion counts as mastered only when you can perform the technique cleanly and identify and explain the structures on the actual specimen. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.